Infectious diseases caused by human acquired immunodeficiency virus (HIV), which is a type of retrovirus, have recently become a serious social problem. A compound of 3'-deoxy-3'-azidothymidine is known as a nucleoside compound used in the clinical treatment of HIV-infection. However, this compound has side-effects since it also exhibits considerable toxicity in the host cell.
Although some 2',3'-dideoxyribonucleosides are known as nucleoside compounds exhibiting an anti-retroviral activity, it is still necessary to develop a substance possessing a higher activity and lower toxicity to the host cell (Hiroaki Mitsuya, Bodily Defense, Vol. 4, pp. 213 to 223 (1987)).
On the other hand, various acyclonucleoside compounds have been synthesized since Acyclovir (acycloguanosine) was developed as an antiviral substance effective against herpes virus (C. K. Chu and S. J. Culter, J. Heterocyclic Chem., 23, p. 289 (1986)). However, no acyclonucleoside compound having a sufficient activity especially against retroviruses has yet been discovered.
We have focussed our attention on 6-substituted acyclopyrimidine nucleoside compounds and have synthesized various novel 6-substituted acyclopyrimidine nucleoside derivatives and screened those compounds to detect an effective antiviral agent, especially to the retrovirus. Some 6-substituted acyclopyrimidine nucleoside compounds such as 6-fluoro substituted derivatives, 6-alkylamino substituted derivatives (DD-232492-A) and 6-methyl substituted derivatives (C.A. 107, 129717w (1987)), are known; however, the anti-retroviral activity of these compounds has not been described. As a result of our investigation, it was found that specific 6-substituted pyrimidine nucleoside compounds according to the invention satisfy the above demand which enables one to provide effective anti-retroviral agents.